CVE-2026-25896criticalCWE-185 CWE-79

CVE-2026-25896: critical vulnerability in NaturalIntelligence fast-xml-parser

fast-xml-parser has an entity encoding bypass via regex injection in DOCTYPE entity names

Published 20 Feb 2026 · Updated 10 Sep 2026

28Vexday Risk Score

No sign of exploitation. No public exploitation artifact known so far.

ssvc Trackcvss 9.3epss 0.5%

exploitation probability

0.5%top 59% of all CVEs

observed exploitation

nono source reports it

fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. From 4.1.3to before 5.3.5, a dot (.) in a DOCTYPE entity name is treated as a regex wildcard during entity replacement, allowing an attacker to shadow built-in XML entities (<, >, &, ", ') with arbitrary values. This bypasses entity encoding and leads to XSS when parsed output is rendered. This vulnerability is fixed in 5.3.5.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N

Affected products

NaturalIntelligence · fast-xml-parser

Related CVEs — NaturalIntelligence fast-xml-parser

In the same product, most dangerous first.

CVE-2023-34104HIGHRegex Injection via Doctype EntitiesEPSS 1.1%CVE-2026-26278HIGHfast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)EPSS 1.0%CVE-2024-41818HIGHReDOS at currency parsing fast-xml-parserEPSS 0.8%CVE-2026-33036HIGHfast-xml-parser affected by numeric entity expansion bypassing all entity expansion limits (incomplete fix for CVE-2026-26278)EPSS 0.7%CVE-2026-27942LOWfast-xml-parser has stack overflow in XMLBuilder with preserveOrderEPSS 0.7%CVE-2026-25128HIGHfast-xml-parser has RangeError DoS Numeric Entities BugEPSS 0.6%

References